Evaporator structure and method of manufacture



Jan. 12, 1960 A. G. JANOS 2,920,377

EVAPORATOR STRUCTURE AND METHOD OF MANUFACTURE 'Filed 0017. 12, 1956F|G.l FIG.2

INVENTOR.

'3 ALFRED G. J'ANOS BY ,Z/KW

HIS ATTORNEY United States Patent Alfred G. Janos, Louisville, Ky.,assignor to General Electric Company, a corporation of New YorkApplication October 12, 1956, Serial No. 615,694 2 Claims. (Cl. 29-1555)The present invention relates to evaporator structures of theroll-bonded type and more particularly to the method of manufacturingsuch a structure.

Various methods and means have heretofore been provided to eliminate thecoating of frost that accumulates on an evaporator which is being usedto remove heat from a surrounding, relatively warmer atmosphere, such asis illustrated by the evaporator of a refrigerator. Many previousattempts to solve this problem have ultilized a heater that ispositioned closely adjacent the evaporator structure for periodicallyheating the structure to melt the accumulated frost and ice. Inevaporators of the roll-bonded type, it has been the practice to clamp aheating wire to the surface of the sheet, making several passes of thewire along the sheet to provide the necessary heat transfer. In theabove type of apparatus, heat transfer is very poor between the heatingwire and the roll-bonded sheet because the heat is transferred to thesheet by direct contact with the heating Wire at only one point on thecircumference of the wire. The remaining heat, transferred by convectioncurrents, is very poor. The heat transfer can sometimes be improved bythe provision of a masking material around the outer portions of thewire for preventing the escape of heat in directions away from theevaporator structure. Another disadvantage of the above type ofdefrosting arrangement is that the heating wire is in an unprotectedposition adjacent the evaporator and can be easily damaged.

It is an object of the present invention to provide a method ofmanufacturing an improved evaporator structure having a heater wirepositioned therein, and forming an integral part thereof.

Further objects and advantages of the invention will become apparent asthe following description proceeds, and the features of novelty whichcharacterize the inven tion will be pointed out with particularity inthe claims annexed to and forming a part of this specification.

In carrying out the objects of this invention there is provided anevaporator structure in the form of a rollbonded sheet of metal having apair of separate passages formed therein. One of the passages isprovided for conducting a refrigerant for heat transfer purposes. Aheater wire which is completely enclosed within the second passage andconnected to a means for supplying an electrical current thereto isprovided for periodic defrosting of the heat exchange structure. Theheat exchange structure is formed by roll-bonding into a single sheet,two sheets of metal having between them a stopweld material arranged intwo separate paths. By applying a fluid under pressure to the areaswhich were prevented from forging by the stop-weld material, thenonforged portions are expanded to form two separate passages within thesheet. After slitting one of the passages lengthwise along its expandedportion and bending outwardly the tabs formed thereby, a heater wire isin-' serted into the passage. By bending the tabs back into ice 2 place,the heater wire is clamped into position within the heat exchangestructure.

For a better understanding of the present invention reference may be hadto the accompanying drawings in which:

Fig. 1 is a plan view of an evaporator structure incorporating thepresent invention;

Fig. 2 is an elevation view illustrating the roll-bonding of two sheetsinto one by hot rolling;

Fig. 3 is edge view of a sheet of roll-bonded metal taken along line 33of Fig. 1;

Fig. 4 is a cross sectional view of a roll-bonded sheet having anexpanded passage and a slitting mechanism;

Fig. 5 is a cross sectional view taken along line 44 of Fig. 3; and

Fig. 6 is a cross sectional view similar to Fig. 5 taken along the line66 of Fig. 1.

Referring now to Fig. 1 there is shown an evaporator structureincorporating the defrost arrangement of the present invention. Theevaporator comprises a sheet 1 of thermally conducting material, such asan alloy of copper or aluminum. The single sheet 1 has been formed froma pair of identical sheets 2 and 3 by a roll-bonding or roll-forgingprocess well known in the art, as illustrated in Fig. 2. The sheet 1 isprovided with a pair of continuous passages, integrally formed therein.Thus, as can be seen in Fig. 1, the sheet 1 is provided with a passageor refrigerant conduit 4 for carrying a suitable refrigerant and asecond passage or heater conduit 5 into which a heater wire 6 isinserted. The refrigerant passage 4 forms a serpentine configurationupon the sheet 1 and is provided with openings7 and 8 at one edge 9 ofthe sheet. It is obvious that the refrigerant passage can take on anydesired configuration so long as there are two openings somewhere on thethermally conducting sheet 1. It is contemplated that during theoperation of the heat exchanger the openings 7 and 8 will be connectedin refrigerant flow relationship with a suitable compressor (not shown)and condenser (not shown).

The heater passage 5 is provided with a plurality of fingers 11extending adjacent to and between the convolutions formed by therefrigerant passage 4. The specific configuration of the heater passagewill be dependent upon the configuration of the refrigerant passage, butit is desirable for defrost purposes that the heater passage lieadjacent to as much of the refrigerant passage as possible. As can beseen in Fig. 1, the heater passage has an opening 12 in the edge 9 ofthesheet of thermal conductive material. As illustrated by the dotted linepositions shown in Fig. 1, the heater wire 6 forms a completed circuitwithin the heater passage 5, entering at the edge of the sheet 9 throughthe opening 12 and also exiting at this point. Thus, referring to Fig.6, a double strand of heater wire 6 is provided throughout the heaterpassage 5.

In operation the heater wire 6 will be connected in series with a meansfor applying an electrical current thereto at those times whendefrosting of the refrigerant carrying passage is found necessary. Ascan best be seen in Fig. 6 the arrangement of the heater wire .6 withinthe passage 5 provides a very efiicient heat transfer arrangementbetween the wire 6 and the heat exchange structure 1. When an electricalcurrent is passed through the wire 6 and heat is generated thereby, theonly possible means for transferring the heat away from the wire 6 isthrough the walls 13 and 14 which completely surround the wire 6. Heatis then transferred by direct conduction along the sheet 1 to thevarious portions of the refrigerant passage 4. With this arrangement itis possible to reduce the defrost time to a minimum with a minimum lossof power due to heat dissipation.

,process. a A stop-weld or weld-preventing material of a type well knownin the art, such asa mixture or graphite -in'water glass,is then appliedin a thin layer to selected areas on the face of one of the sheetsaccording to a predetermined pattern. Such weld-preventing material maybe sprayed through a masking die, or painted through a stencil, orapplied in any other suitable manner. The pattern for applying theweld'preventing material may be of almost any desired configuration solong as it comprises a pair of separate paths which do not come intocontact at any portion of their configuration. One of the paths must beexposed on at least two points around the edge of the sheet. This pathwill later be expanded to form the refrigerant carrying passage 4.Theother path must be exposed on at least one point around the edge of'the sheet and will later be expanded to form the heater carrying passage5. V

After the pattern of weld-preventing material 15 has been applied to oneof the sheets, the sheet 3 is placed on sheet 2 with the weld-preventingmaterial 15 between them. This assembly is then roll-bonded orroll-forged by means well known in the art, as illustrated in Fig. 2, toform the single sheet 1. I In order to roll-forge the assembly, thesheets 2 and 3 are first fastened together to avoid obliteration of thepattern. This may be done by any suitable means, such as heating orwelding the edges, tacking the edges together by spot welding, orcrimping the edges, or the like. The assembly is then placed in afurnace and heated to a temperature sufliciently high to effect pressurewelding of'the two sheets of metal in the hot-rolling step illustratedin Fig. 2. The exact temperature to be used for pressure welding is, ofcourse, dependent upon the melting point of .the particular metal oralloy utilized and should be relatively close thereto. After thehot-rolling step described above, it is sometimes necessary to cold-rollthe sheet in order to accurately control the thinness of the sheet. Ifthis is the case it is sometimes necessary to anneal the finished sheetto reduce the stresses set up during the cold-rolling process. 7

During the rolling process, the portions of the sheets 2 and 3 adjacentthe pattern or area covered by the weldpreventing material are preventedfrom'forging together into a single sheet. After the rolling and othersuch processing has been completed, the unbonded portions are thenexpanded by applying a fluid pressure. This is accomplished bymechanically prying open the unbonded portions formed at points 7', 8and 12 in the edge 9 of the sheet 1, as can be seen in Fig. 3. A veryhigh fluid pressure is applied, through use of a plurality of tubes ofcopper or other suitable tubular material (not shown) connected at oneend to a source of very high fluid pressure and having the other end'orends inserted into the openings at points 7*, 8 and 12 and brazed orthreaded therein. As will be understood by those familiar with the art,the amount of fluid pressure necessary Will vary with the gage, temper,and composition of the metal used but sufficient pressure is applied toexpand the metal in the unwelded or unbonded inner portions adjacent theweldpreventing material. Upon application of the desired fluid pressurethe refrigerant and'heater carrying passages 4 and 5 respectively, areformed.

In order to insert the aforementioned heater wire 6 into the heatercarrying passage or conduit 5 formed by applying pressure to theroll-bonded sheet 1, it is necessary to slit one of the expanded walls14 of the passagelengthwise along the length of the passage. This isperformed by a cutting arm 16 carrying a cutting tool 17 which isinserted into the heater passage 5 at the end thereof and traversed thelength of the passage. Thus, as can be seen in Fig. 4,;the cutting tool17, inserted into the pas- I sage 5 and traversed the length thereof,slits the upper 19 are shown in Fig. 5. It. is necessary to turn thetabs 7 18 and 19 outwardly in order to provide an opening through whichthe heater wire 6 may be inserted. By the proper design of the cuttingtool 17, it is possible to turn the tabs 18 and 19 outwardly during theslitting operation. This may be performed, however, as a separateoperation by passing a properly designed tool along the slit formed inthe wall 14 of the heater passage. In order to slit the entire length ofthe heater passage and thereafter turn the tabs outwardly, it might benecessary according to the particular configuration of the heaterpassage, to make several cutting and turning passes with the cutting andturning tools. Thus, for the configuration shown in Fig. 1 it would benecessary to make four passes for. each operation, one for each of theupwardly extending fingers 11 and one along the base portion 21 of theheater passage. 7

After the tabs 18 and 19 have been turned outwardly from the heaterpassage 5', the next step is to insert the heater wire 6 within thepassage. As shown in the illustrated embodiment of the invention, theheater wire forms a continuous loop through the heater passage 5 andprovides a' completed electrical circuit therein. This particulararrangement for the heater wire is not considered absolutely essentialto the invention, and it could take on .many forms depending ontheconfiguration of the heater passage, such as a single wire extending thelength of a continuous passage having two openings somewhere around theedge 9 of the sheet 1.

After the heater wire 6 has been inserted, the tabs 18 and 19 are bentback into their original position thereby retaining the heater wire inplace within the passage 5. This operation may be accomplished in any ofa number of different ways such as by rolling, stamping, pressing or thelike as long as the heater wire 6, positioned within the passage, is notdamaged.

By the present invention there has been provided a method ofmanufacturing an evaporator structure having a heater wire, defrostingmeans arranged to promote heat transfer of maximum efficiency betweenthe wire and the heat exchange structure. Furthermore the methodoutlined above provides a simple, low-cost process for manufacturing theabove-described evaporator.

While in accordance with the patent statutes there has been describedwhat'at present is considered to be the preferred embodiment of thisinvention, it will be obvious to those skilled in the art that variouschanges and modifications may be made therein without departing from theinvention and it is, therefore, the aim ofthe appended claims to coverall such changes and modifications as fall within the true spirit andscope of the invention.

What I claim as new and desire to secure by Letters Patent of the UnitedStates is:

1. In a method of forming an evaporator having defrost means, the stepscomprising superimposing one upon the other'two sheets of metal having astop-weld material arranged therebetween in \at least two separatesages, slitting one of said passages lengthwise along the length of saidpassage thereby forming tab portions adjacent said slit, turning saidtab portions of said' slit passage outwardly, inserting. a heater wireinto said slit. passage, and bending said tab portions of said passageback into their original position to completely enclose said heater Wirewithin said passage whereby an electric current whenpassed through saidheater wire willeifect defrosting of said evaporator. c r

2. In the method of forming an evaporator having defrost means, thesteps comprising superimposing one upon the other two sheets of metalhaving a stop-Weld material arranged therebetween in at least twoseparate and continuous paths, one of said paths having the ends thereofexposed on at least one edge of said sheets, the other of said pathshaving an end exposed on one edge of said sheets, roll-bonding said twosheets into one by rolling the sheets at a temperature sufiiciently highto cause said sheets to completely forge together into one except wheresaid stop-Weld material has been arranged, applying a high fluidpressure to separate said non-forged portions of said sheets to form apair of continuous passages, slitting one of said passages along thelength of said passage thereby forming tab portions adjacent said slit,turning said tab portions of said one passage outward- 1y, inserting aheater wire into said slit passage, and bending said tab portions ofsaid passage back into their origi- References Cited in the file of thispatent UNITED STATES PATENTS 2,375,334 Valyi et al. May 8, 19452,677,172 Oakley May 4, 1954 2,690,002 Grenell Sept. 28, 1954 2,701,410Huck et al. Feb. 8, 1955 2,716,179 Cornella Aug. 23, 1955 2,755,371Jackson July 17, 1956 FOREIGN PATENTS 60,792 Denmark Apr. 12, 1943

